popenCPP.cc

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// original code by the Minima Authors under the MIT license. See AUTHORS for the list of authors.

#include "popenCPP.h"
#include "FWCore/Utilities/interface/Exception.h"
#include <cstdio>
#include <string>
#include <istream>

namespace {
  class fbuf final : public std::streambuf {
    FILE *file;
    char *buf;
    constexpr static size_t bufsz = 4096;

  public:
    fbuf(FILE *f);
    ~fbuf() override;

  protected:
    std::streambuf *setbuf(char_type *s, std::streamsize n) override;
    int sync() override;
    int_type underflow() override;
  };

  class cfstream final : public std::istream {
    fbuf buf;

  public:
    cfstream(FILE *f);
  };
}  // namespace

std::unique_ptr<std::istream> reco::exprEvalDetails::popenCPP(const std::string &cmdline) {
  FILE *f = popen(cmdline.c_str(), "r");
  if (!f)
    throw cms::Exception("PopenCPP", "(\"" + cmdline + "\") failed");
  return std::unique_ptr<std::istream>(new cfstream(f));
}

fbuf::fbuf(FILE *f) : file(f), buf(new char[bufsz]) { this->setg(this->buf, this->buf + bufsz, this->buf + bufsz); }

fbuf::~fbuf() {
  delete[] this->buf;
  pclose(this->file);
}

std::streambuf *fbuf::setbuf(char_type *s, std::streamsize n) { return nullptr; }

int fbuf::sync() {
  if (fflush(this->file) != 0)
    return -1;
  return 0;
}

fbuf::int_type fbuf::underflow() {
  if (this->gptr() < this->egptr()) {
    char c = *this->gptr();
    this->setg(this->eback(), this->gptr() + 1, this->egptr());
    return traits_type::to_int_type(c);
  }
  size_t n = fread(this->buf, 1, sizeof(this->buf), this->file);
  if (n == 0)
    return traits_type::eof();
  this->setg(this->buf, this->buf, this->buf + n);
  return traits_type::to_int_type(*this->gptr());
}

cfstream::cfstream(FILE *f) : std::istream(&buf), buf(f) {}